A secondary battery receives much attention as a power source of an electric vehicle (EV), a hybrid electric vehicle (HEV), a parallel hybrid electric vehicle (PHEV), etc., suggested as a means for solving the air pollution, etc. of a common gasoline vehicle, a diesel vehicle, etc. using a fossil fuel. In a medium and large size device such as a vehicle, high power and high capacity are necessary, and a medium and large size battery module in which a plurality of battery cells are electrically connected is used.
However, since the medium and large size battery module is preferably manufactured to have a small size and light weight, a polygonal battery, a pouch shape battery, etc. having high stacking degree and light weight when considering capacity are mainly manufactured as the battery cell of the medium and large size battery module.
In general, an electrode assembly includes a stacked structure of cathode/separator/anode and is manufactured by arranging a plurality of cathodes 1 and anodes 2 on a separator sheet 3 as shown in FIG. 1, and wrapping from one terminal portion of the separator sheet 3 (for example, from the cathode 1 at the rightmost in FIG. 1) sequentially counterclockwise. However, in this structure, temperature gradient may be generated between an electrode at the center portion and an electrode at the outer portion, thereby generating different heat emitting efficiencies. Thus, lifetime may decrease after use for a long time.
Alternatively, as shown in FIG. 2, an electrode assembly is composed of alternately stacked cathodes 1 and anodes 2 with a separator sheet 3 therebetween in zigzags. This method (referred to as a Z-folding method) is disclosed in Korean Publication Patent No. 2000-0051741.
According to the above described method of manufacturing an electrode assembly, a cathode and an anode are stacked one by one, and a process for the completion of one electrode assembly is time-consuming. Thus, the productivity of an electrode assembly is markedly lowered. In addition, as the number of electrodes necessary for a secondary battery increases, the generation of defects concerning position alignment between cathodes and anodes during folding may markedly increase. Further, a folding equipment is required to increase in line with the production capacity of the electrode assembly, and so, manufacturing costs may increase. Thus, developments on an electrode assembly having improved productivity and good position alignment between cathodes and anodes, and a manufacturing method thereof are necessary.